Basics of Echocardiography

Transcript of the video: Echocardiography is now not restricted to the echocardiographic laboratory. It is used in the emergency department, at bedside, in the intensive care unit as well as in the operating room. Hence a basic knowledge is needed for all physicians and paramedics. During echocardiography, a transducer transmits the ultrasound beam towards the heart. Echoes received by the transducer from various structures of the heart are analysed by the echocardiograph and a graphical representation
displayed on the monitor.

Location of the transducer is at the top of the image sector. Structures nearer to the transducer are shown at the top of the image and those away from the transducer at the bottom of the image. The image shown here is an animated 2 dimensional echocardiogram.

This one is an older mode known as time-motion mode or M-Mode echocardiogram. Unlike the previous 2 dimensional imaging, this is a single dimensional imaging. Movement of the structures along a single
scan line are depicted as a horizontal graph. Though it is the oldest mode of echocardiography,
it is still being used for taking measurements of the left ventricle.

Doppler echocardiography uses the Doppler principle and targets the moving red blood cells. The velocity at each point is depicted as a spectral tracing. In Pulsed Doppler, intermittent pulses are sent, and echoes received. In Continuous wave Doppler, the signals are sent and received continuously.

Flow away from the transducer is depicted below the baseline and those towards the transducer are depicted above the baseline. When the velocity is beyond the limit of the Doppler mode used, the upper part is cut off as can be seen above the baseline in this case.

The remaining part is shown below the baseline. This is known as aliasing and wrap around. The direction of flow is difficult to interpret then. In such situations, continuous wave Doppler
with higher velocity range is used.

An intermediate option is HPRF or high pulse repetition Doppler. Disadvantage of continuous wave is that it cannot pinpoint the exact location of the high velocity signal as it is continuously transmitting and receiving echo signal. Displaying Doppler flow information on a two dimensional image is known as colour flow mapping or color Doppler imaging.

Here one image is two dimensional another has colour flow information in a sector. Blue colour represents flow away from the transducer and red colour flow towards the transducer. It has nothing to do with the colour of the blood like oxygenated or deoxygenated.

While conventional Doppler images the velocity of blood, same principle applied to the myocardium is known as tissue Doppler imaging. Tissue Doppler information overlayed on two dimensional image is known as colour kinesis, which can be seen in the inset at the top of this image.

Tracing in the lower part is tissue Doppler imaging from the medial mitral annulus. The images shown so far were from transthoracic echocardiography.

Another mode is transesophageal echocardiography in which the echo probe at the tip of an endoscope like device is introduced into the esophagus. As the esophagus is just posterior to the heart, image quality is excellent. Shorter distance permits the use of higher frequency transducers which give better image resolution. Higher frequency transducers have only low depth penetration and are not suitable for transthoracic echocardiography.

The four common locations at which the echocardiographic transducer is placed for imaging are the parasternal, apical, subcostal, and suprasternal. Parasternal views are often obtained first, followed by apical, subcostal, and suprasternal. A good knowledge of the anatomy of the heart is needed for interpretation of images from each view.

This becomes more difficult in complex congenital heart diseases where the cardiac chamber positions and size may vary. First view to be obtained is often the parasternal long axis view. This view images the heart from the base to apex long axis view.

Transducer is placed in the left parasternal region and fine adjustments in angulation are made till a view similar to that in the left panel is obtained. Exact position and angulation will vary between individuals.

Usual structures imaged in this view are the right ventricular free wall and outflow region, interventricular septum, aorta, and aortic valve, left ventricular outflow tract, anterior and posterior mitral leaflets, left ventricular cavity, posterior wall of left ventricle and left atrium.

Colour Doppler imaging is used to image the flow directions and abnormal flows if any. Here is an animated view from the parasternal long axis.

Opening and closing movements of the aortic and mitral valves are visible. Contraction of each region of the left ventricle is also inspected closely for any abnormalities of regional wall motion.

Parasternal short axis view is obtained by rotating the transducer almost at right angle in the same location so that the echo beam is perpendicular to the base apex axis of the heart.

Three cuts are usually obtained in this view. The aorta, right ventricular outflow tract and pulmonary artery up to its bifurcation is imaged in the upward angulation shown in the left panel. Colour flow shows the flow in pulmonary artery. Slight downward angulation of the transducer from this view gives the left ventricular cross section with mitral valve cross section within. Right ventricular cavity is elliptical in
this view and left ventricular cavity is circular. Wall motion of the left ventricle can be assessed in this view also. Planimetry of mitral valve area can be obtained in parasternal short axis view in case of mitral stenosis.

Apical views are obtained by keeping the transducer directly over the apex beat. Apical four chamber, two chamber and three chamber views can be obtained by rotating the transducer. Apical four chamber view is illustrated here. Apical four chamber view shows all four cardiac chambers, mitral and tricuspid valves, and the septa. But as the echo beam is parallel to the interatrial septum, false echo drop outs can occur in the interatrial septum.

Apical five chamber view including the proximal aorta can be obtained by slight tilting of the transducer from this view. Subcostal view is obtained from below the xiphisternum in the epigastrium. Transducer rotation is needed to get subcostal four chamber and short axis views. Interatrial septum is best imaged in this view.

Assessment of the inferior vena cava for checking the hydration status is also feasible from this view. Subcostal view is a favourite view of pediatric echocardiographers.

Suprasternal view is useful in imaging arch of the aorta and nearby regions of ascending and descending aorta. Coarctation of aorta and patent ductus arteriosus can be imaged in this view. The image shows the blue coloured descending aortic flow on colour Doppler. Gradient of coarctation can be assessed in
this view.

Apart from these standard views, other modified views may also be used in certain circumstances. A right parasternal view may be used when the heart is enlarged, to assess the tricuspid regurgitation jet. Dilated ascending aorta will also be visible in a right parasternal view.

An annotated video of normal colour Doppler echocardiogram illustrating various views and an M-Mode tracing is shown here.

[Initially there is two dimensional view from parasternal long axis view followed by colour Doppler and M-Mode. Parasternal short axis view, apical four chamber view and suprasternal view follows.]